Another vote for the tortilla with peanut butter, banana, and put in some sliced almonds for a little crunch.
Depending on their tastes, I make a thai chicken tortilla - grill chicken and then chop it up and toss with thai peanut sauce. Roll into the tortilla with shredded carrots, shredded red cabbage (both shreds can be bought pre-shredded), and shredded mozarella cheese.
You can also do tons of other variations:
italian - chicken, pizza sauce, mozzarella cheese and any veggie toppings (peppers, onions, pepperoni, diced tomatoes, etc.)
mexican - chicken, salsa or taco sauce, smashed avocado, diced tomatoes, shredded lettuce, cheese
greek - chicken, balsamic vinaigrette dressing, feta cheese, shredded lettuce
turkey sandwich - lunchmeat turkey, hummus or smashed avocado, spinach or lettuce, cheese of choice
vegetarian - hummus or avocado, peppers, sprouts, spinach, cheese (depending on how hard core vegetarian/vegan you want to be)